1. Field of the Invention
The present invention relates to a technology for transmitting/receiving signals through precoding in a mobile communication system, and more particularly, to a method for a user equipment to precode and transmit an uplink signal efficiently in a 4-antenna system and a method for a base station to receive the transmitted signal efficiently.
2. Discussion of the Related Art
In a multi-antenna or MIMO system, precoding provides high peak/average system throughput by providing a beamforming gain and a diversity gain to a transmitting/receiving side. Yet, a precoding scheme needs to be appropriately designed in consideration of antenna setting, channel configuration, system structure and the like.
Generally, an MIMO system performs precoding to minimize complexity and control signaling overhead using a codebook based precoding scheme. In this case, a codebook includes a scribed number of precoding vectors/matrixes predetermined between transmitting and receiving sides according to a transmission rank and the number of antennas. The transmitting side selects a specific vector/matrix within the codebook according to channel status information received from the receiving side, perform precoding on a transmission signal, and then transmits the precoded signal. Occasionally, the transmitting side selects a precoding matrix according to a predetermined rule instead of receiving the channel status information from the receiving side, performs precoding and is then able to transmit a corresponding signal.
FIG. 1 is a diagram for explaining a basic concept of codebook based precoding.
According to a codebook based precoding scheme, as mentioned in the foregoing description, a transmitting side and a receiving side share codebook information including a prescribed number of precoding matrixes predetermined according to a transmission rank, the number of antennas and the like with each other. The receiving side measures a channel status via a received signal and is then able to feed back preferred precoding matrix information to the transmitting side based on the aforesaid codebook information. FIG. 1 shows that the receiving side transmits preferred precoding matrix information per codeword to the transmitting side, for example.
Having received the feedback information from the receiving side, the transmitting side is able to select a specific precoding matrix from the codebook based on the received information. Having selected the precoding matrix, the transmitting side performs precoding in a manner of multiplying layer signals, of which number corresponds to a transmission rank, by the selected precoding matrix. And, the transmitting side is able to transmit the precoded transmission signal via a plurality of antennas. Having received the signal precoded and transmitted by the transmitting side, the receiving side is able to reconstruct the received signal by performing a process reverse to the precoding performed by the transmitting side. As a precoding matrix generally meets such a condition of a unitary matrix (U) as U*UH=I, the reverse processing of the above precoding can be performed in a manner of multiplying a received signal by Hermitian (PH) of a precoding matrix (P) used for the precoding of the transmitting side.
In LTE (3RD Generation Partnership Project Long Term Evolution) release 8 system, in case of applying MIMO scheme to an uplink signal transmission to a base station from a user equipment, an MIMO transmission scheme is prescribed for a downlink signal transmission from a base station to a user equipment only due to such a problem as PAPR/CM (peak-to-average ratio/cubic metric) property degradation and the like. Yet, an uplink signal transmitted by a user equipment to a base station is ongoing to be discussed in a direction of applying MIMO scheme for transmission rate increase, diversity gain acquisition and the like. And, a next standard of 3GPP LTE system is ongoing to discuss about a detailed method of applying MIMO scheme to an uplink signal transmission.